1. Field of the Invention
The present invention relates generally to design tools for designing optical networks. More particularly, the present invention is directed towards a design tool for selecting the placement of optical amplifiers in the nodes of a dense wavelength division multiplexed (DWDM) optical network.
2. Description of Background Art
Dense wavelength division multiplexed (DWDM) networks are of interest for a variety of applications, such as a metro area networks. FIG. 1 shows an exemplary prior art metro area network that is a ring network, although it will be understood that a variety of other network topologies are known in the art, such as linear and mesh topologies. Referring to FIG. 1, a DWDM optical network 100 typically comprises a plurality of optical nodes 130 coupled together by optical fibers 140. The group of optical fibers coupling two nodes is commonly known as a span. In metro area network (MAN) and regional area network applications the location of each optical node 130 is typically proximate a desired tributary service center (e.g., at a university, company, business park, etc.) Optical fiber 140 may correspond to pre-existing optical fibers already laid in the ground. Typically, the length and attenuation of the optical fibers 140 of each span of a MAN may vary over a wide range depending upon where the nodes are placed and the pre-existing fibers that are available to couple the nodes.
In a typical DWDM node the multiplexing/demultiplexing required to perform add, drop, and pass-through functions is commonly performed using several stages of multiplexers and demultiplexers. A common node design is to form a multi-stage add/drop multiplexer from a combination of mux/demux modules (also commonly known as “circuit packs”). The total number and placement of optical amplifiers in the nodes of the optical network needs to be selected to achieve a desired quality of service (QOS). Commonly, each input fiber to a node may have coupled to it either zero or one optical pre-amplifier and each output fiber may have either zero or one optical post-amplifier coupled to it.
As shown in detail for Node 1 and Node 3, each optical node 130 may include optical multiplexers/demultiplexers and other elements arranged to permit wavelength channels to pass through the node, wavelength channels to be added in the node, and wavelength channels to be dropped in the node. For example, optical band filter packs 150 and channel filter packs 160 in each node may be configured as add channels at nodes, drop channels at nodes, and pass through selected channels. Wavelength conversion interfaces 170 may be configured to detect the channel and generate an optical signal for a tributary network 180. Additionally, as indicated in Node 2, an optical node may include one or more optical amplifiers such as optical pre-amplifiers 190 (for channels entering the node) and optical post-amplifiers 195 (for channels exiting the node). Typically, a node is adapted to receive at least one optical pre-amplifier 190 for each input port of the node and at least one optical post-amplifier for the output port of the node.
Optical amplifiers, such as erbium doped fiber amplifiers (EDFAs) and semiconductor optical amplifiers (SOAs), are expensive and inject optical noise into the optical network. Consequently, it is desirable to select a minimal number of optical amplifiers necessary to achieve the optical amplification to achieve a desired quality of service (QOS). However, in MAN and regional area network applications the precise number and arrangement of optical amplifiers will depend on the particular network configuration and the services provided.
There is increasing interest in design tools to facilitate the design of optical networks, such as metro area networks. A user-friendly design tool would permit a network to be designed in a reasonable length of time with the resources of a conventional workstation or server. However, as DWDM networks have become more complex and include more optical nodes it is impractical to use conventional analysis techniques to design an optical network to have a minimal number of optical amplifiers and the desired QOS. This has serious implications, since the lack of an effective design tool may result in greater cost and reduced performance of the optical network than could be otherwise obtained if an automated design tool optimized the number and arrangement of optical amplifiers.
What is desired is a new system and method for designing optical networks having a large number of possible optical amplifier arrangements.